use v5.12;
my $check = "a";
$check++ for 1..3; # three letters
say $check;
$check++ for 1..24; # another 24 letters, but there's only 26 in the alphabet,
say $check; # so what happens now we've run off the end?
# hmmm... that's handy.
# it takes us to the next part of your question...
my $input = $check;
my $output = substr($input, 1, 1); # skip one character, take one character
say $output;